The present invention relates to power combiners and splitters. It finds particular application in conjunction with impedance transforming power combiners and splitters, and will be described with particular reference thereto. It will be appreciated, however, that the invention is also amenable to other like applications.
Impedance transformation networks arc utilized in radio frequency ("RF") circuitry to step up or step down the impedance level between pairs of ports for input and output circuits having different source and load impedances, respectively. The impedance transformation network is typically arranged so that the load impedance provided to the input circuit by the impedance transformation network matches as nearly as possible the source impedance of the input circuit. Similarly, the network is arranged so that the source impedance provided to the output circuit by the impedance transformation network matches as nearly as possible the load impedance of the output circuit. Impedance matching is desirable since under these conditions there is a maximum power transfer and a minimum of signal distortion and/or reflection between the input and output circuits.
Power dividers and combiners are useful in a wide variety of circuits. Specific applications include combining multiple power amplifier stages in order to achieve a desired high power output. Since most solid state power devices, such as MESFETs, PHEMTs, and bipolar transistors have low input and output impedances, successive impedance transformations are often necessary to achieve 50 ohm input and output impedance levels.
There are several technologies currently available that provide power combining/splitting, including radial combiners, split lines and branch line combiners.
For example, a power combiner/splitter known as the Wilkinson power combiner/splitter offers binary combining/splitting (i.e., successive multiplications or divisions by two (2)). However, the Wilkinson power combiner/splitter is limited in that the multiplications/divisions are always by a factor of two (2). Furthermore, the input and output impedances are all equal to a characteristic impedance Z.sub.0. The Wilkinson design does not facilitate the use of different input and output impedances regardless of whether it is used as a combiner or a splitter. Since the Wilkinson power combiner/splitter uses quarter-wavelength lines in each multiplication/division and is binary, each multiplication/division past the first requires space for the additional quarter-wavelength lines. Moreover, the Wilkinson power combiner/splitter does not offer N-way combining.
While conventional power combining/splitting methods and apparatuses are suitable for many applications, they do not provide for selective power combining/splitting any number (e.g., N-way) of RF input signals into a single RF output.
The present invention provides a new and improved apparatus and method which overcomes the above-referenced problems and others.